Flexible Functional Split and Power Control for Energy Harvesting Cloud Radio Access Networks

TL;DR

This paper proposes a flexible functional split and power control strategy for energy harvesting cloud radio access networks, optimizing throughput under energy and fronthaul constraints, with a novel online policy that adapts to energy randomness.

Contribution

It introduces a joint optimization framework for functional split modes and power control in renewable-powered C-RAN, including offline analysis and a practical online heuristic policy.

Findings

Flexible functional split significantly improves throughput.

The heuristic online policy performs close to the optimal.

Energy harvesting constraints are effectively managed with the proposed approach.

Abstract

Functional split is a promising technique to flexibly balance the processing cost at remote ends and the fronthaul rate in cloud radio access networks (C-RAN). By harvesting renewable energy, remote radio units (RRUs) can save grid power and be flexibly deployed. However, the randomness of energy arrival poses a major design challenge. To maximize the throughput under the average fronthaul rate constraint in C-RAN with renewable powered RRUs, we first study the offline problem of selecting the optimal functional split modes and the corresponding durations, jointly with the transmission power. We find that between successive energy arrivals, at most two functional split modes should be selected. Then the optimal online problem is formulated as an Markov decision process (MDP). To deal with the curse of dimensionality of solving MDP, we further analyze the special case with one instance of energy arrival and two candidate functional split modes as inspired by the offline solution, and then a heuristic online policy is proposed. Numerical results show that with flexible functional split, the throughput can be significantly improved compared with fixed functional split. Also, the proposed heuristic online policy has similar performance with the optimal online one, as validated by simulations.